Telephone-exchange system



July 23, 1929. H. E. BRAGG 1,722,033

TELEPHONE EXCHANGE SYSTEM Filed Oct. 18. 1927 LAP/ZED J A TTOR/VEYPatented July 23, 1929.

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HERBERT E. BRAGG, OF EAST ORANGE, NEW JERSEY, ASSIG-NOR TO BELLTELEPHONE LAB RJ IORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATIONOF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed October 18, 1927. Serial No. 226,849.

This invention relates to telephone exchange systems and particularly tomessage registration on party lines. v

The object is to secure greater reliability in the tests made on partytelephone lines to discriminate between the substations thereof.

A feature of the invention is a system in which one substation of aparty line is distingushed from others by means of a device connected inthe talking circuit at the sub station and arranged to allow current toflow in one direction in a circuit including the line conductors inseries, but to offer substantial resistance to flow in the oppositedirection.

Another feature of the invention is an arrangement at the central officefor testing a calling party line by first connecting a source ofpotential in series with the line loop in one direction and thenreversing the connection. The current flowing under these conditions isused to distinguish between substations and to cause selective operationof message registers.

The drawing shows the invention applied to a four-party line in anautomatic telephone system. At the left of the drawing is shown asubscribers line 6 having four substations A, B, C and D.

The substation A is provided with a device 1 which permits currenttoflow in one direction upon the application of relatively low potentialsand substantially prevents the flow of current in the oppositedirection. The device 1 is illustrated schematically and it is to beunderstood that any suitable device of this character may be'used. Forexample, a rectifier ot the type shown and described in the Journal ofthe American Institute of Electrical Engineers for March 1927, page 215,may be employed.

T he rectifier or uni-lateral device 1 is eon nected directly inserieswith the talking circuit as shown. The other three substations B,C and D are equipped with space discharge devices 2, 3, 4t and 5. Thearrangement of these devices is such that for a given voltage currentflows from one electrode to the other, but substantially no current willflow in the reverse direction. The station B is equipped with two ofthese devices oppositely con- "nected so that current of one polaritywill flow through re device to and. cur

rent of the opposite polarity will flow through the other device toground. Stations C and D are provided each with a single device, one ofwhich is connected to permit current of one polarity to flow and theother to permit current of the opposite polarity to flow. These devicesmay be of the space'discha'rge type, such as illustrated in theapplication of Gray, Serial No. 98,658, filed March 31, 1926.

At the central ottice the party line terminates in a line finder Fillustrated diagrammatically by the brushes 7 to 12, inclusive. The linefinder F is joined to a selector switch S havingbrushe's 60, 61 and 62.The line finder and selector unit partially shown may be ofsubstantially the same construction and operation as illustrated anddescribed in detail in the patent to'Kopp, No. 1,589,402, is-

'13, 14,15 and 16 are respectively individual to substations A,,B, C andD.

The rotary stepping switch, shown at the right of the drawing, comprisesthe brushes 51 to 55, inclusive, and the stepping magnet- This switchserves as an auxlllary control device. 3

A detailed description will now be given,

assuming that the party at substation D initiates a call. The initiationof the call causes the operation of line finder F to seize thesubscribers line 6. The calling subscriber thereupon manipulates hisimpulse transmitter 65 to set up the designation. of the called line inthe register sender ,(not shown) at the central otlice. Following thisthe sender controls the selector switch S and succeeding switches toextend the connection to the called subsoribers line.

When the called subscriber answers, the relay 19 operates in the usualmanner and at this time the sequence switch 63 has advanced to someposition, such as positionltl. As soon, after the relay l9 operates, as,the

' 35,5 its upper een'taet, a

cuit is completed from battery, through the winding of relay 21, contactof said interrupter, contacts of sequence switch spring 38, contact ofrelay 19, through the sequence switch springs 41 and 40 to ground. Relay21 operates and locks in the circuit from winding of relay 17, outerleft contact of relay 20, spring 43, front contact of relay 21, lowercontact of interrupter 35 and thence to ground as abore traced. Relay1'? operates locks through its middle lower contact and thence throughthe contacts of relay 19 to ground as previously traced.

The auxiliary stepping switch is now set in operation to make a test ofthe calling subscribers line to determine which station has initiatedthe call. The circuit for operating the stepping switch leads fromground through the interrupter 33, lower contact of relay 17, wiper 51,winding of the stepping magnet 64'to battery. Magnet 64 energizes 'tostep the wipers 51 to 55, inclusive, to their second position terminals.

In position 2 of the switch a preliminary test is made to'deterinine ifan accidental ground on the line initiated the operation of the centraloffice equipment. This test is made by means of a circuit from thepositive pole of grounded battery through the wind ing of relay 25,thence through wipers 52 and 53 in parallel through the front contactsof relay 17 to the tip and ring conductors of the subscribers line. Thecall being a genuine one, no low resistance ground or foreign potentialexists on either'the tip or ring conductors of the line and relay 25does not operate. The potential of the battery applied to the line inthis test circuit is insufiicient to cause current to flow through thespace discharge tubes. While the stepping switch is in position 2, acircuit is completed from battery through the right winding of relay 31,wiper 54 to ground through the springs 41 and 40. Relay 31 operates andlocks through its winding and rightcontact independently of the wiper54.

On the next closure and opening of the interrupter 33, the switchsteps-to its third position. In this position another test is made todetermine which station originated the call. The circuit for this testmay be traced from positive pole of the high potential source 46, lamp47, relay 22, thence in parallel, through the wipers 52 and 53 and thecontacts of relay 17, over the tip and ring conductors of thesubscribers line, through the switchhook contacts to the dischargedevice 5. It will'be assumed that the polarity of the device 5' is suchthat it does not permit the flow of current in the circuit above traced.Accordingly, the relay 22 remains inert.

The stepping switch advances into position 4 where a circuit iscompleted from ground through the resistance 67, and thence in parallelthrough the wipers 52 and 53 to the tip and ring conductors of the line.This connection serves to discharge the subscribers line before applyingpotential in the opposite direction. 3

In position 5 of the stepping switch a test circuit is closed from thenegative pole of grounded battery, through the winding of relay 24,thence through the wipers 52 and 53 to the tip and ring conductors ofthe subscribers line. If the line is still free from a low resistanceground connection, relay 24 remains inert.

In position 6 of the stepping switch, a test circuit is completed fromthe negative pole of the high potential source 48, lamp 49,winding ofrelay 23, wipers 52 and 53 in parallel, thence over the subscribers lineto the substation, In this case the potential is of the proper polarityto cause the flow of current in the circuit through the discharge tube5. Current flowing in this circuit causes the operation of relay 23.Relay 23 in operating closes an obvious operating circuit for relay 28which looks to the contact of relay 31.

In position 8 of the control switch a cir- V cuit is completed from thepositive pole of battery 69 through the right winding of relay 26, wiper52, thence over the tip side of the line through the switchhook contactsof substation D and returning over the ring side of the line throughwiper 53 to the negative pole of battery 69. Current flows in thiscircuit, operating the relay 26, which locks through its left wind-ing.In position 9 of the control switch another circuit is completed fromthe negative pole of battery 69 through the wiper 52 and thence over thesubscriber s circuit and returning through the ;wiper 53, right windingof relay 30 to the positive pole of battery 69. Relay 30 operates inthis circuit and locks to ground.

The control switch advances into position 10 where the relay 20 isenergized in a circuit from battery through its winding, wiper 54,thence through contacts 41 and 40 to ground. Relay 20 locks through itswinding and inner right contact to ground independently of the wiper 54.Relay 20 releases the relay 17 which completes the tip and ringconductors through to the contacts of relay 18. The control switchcontinues to advance till it reaches ing of magnet 64, wiper 55, contactof said magnet to ground at the front contact of relay 20. The magnet 64interrupts its own circuit and steps the switch forward to its normalposition.

At the end of conversation the called party replaces his receiver,resulting in the deenergization of relay 19. In the well known mannerthe sequence switch 63 moves from the talking position to a subsequentposition, such as position 17 to prepare for metering. Relay 19 inreleasing opens the circuit of relay 21 which also releases. Relay 20 isnow held in a circuit from battery through its winding and inner rightcontact, back contact of relay 21, wiper 55, contact of magnet 64 toground at the front contact of relay 20. Relay 31 is also held in acircuit from battery through its right winding and contact and thencethrough the back contact of relay 21 to ground as above traced.

lVhen the sequence switch 63 moves from position to position 17 ametering circuit is completed from battery through the resistance 70,inner left contact of relay 31, contacts of spring 42, inner leftcontact of relay 20, conductor 71, to the right back contact of relay29, right front contact of relay 28, inner right back contact of relay27, brush 12, through the winding of register 16 to ground. The register16 operates and charges the call to the substation D. When the sequenceswitch 63 reaches position 17, and as soon thereafter as interrupter 34closes, a circuit is completed from battery through the winding of relay21, cont-acts 37 and 36 to ground at interrupter 34. Relay 21 operatesand releases the relays and 31.

From this point the release of the line finder and selector takes placein any well known manner such as explained in the patent to Kopp, No.1,589,402, granted June 22, 1926.

Assume next that the call is initiated at the substation C. As in theprevious case neither of the relays 24 and 25 operates. Since thepolarity of the device 4 is opposite that of the device 5, current fro-mthe high potential source 46 is permitted to flow in the test circuitbut not from the high potential source 48. Accordingly the relay 22operates and relay 23 remains inert. Relay 22 closes an obviousoperating circuit for relay 27. Relay 27 locks through its left contact.As before, the relays 26 and both operate.

The metering circuit may be traced as explained, over contactor 71through the right back contacts of relays 29 and 28, outer right frontcontact of relay 27, brush 11 to the winding of register 15 to ground.The reg.- ister 15 operates, charging the call to substation C.

If the call is originated at station B both relays 22 and 23 operatecausing the energization of relays 27 and 28. Also the relays 26 and 30are both energized. The metering circuit in this case leads over theconductor 71, right back contact of relay 29, right front contacts ofrelays 28 and 27, brush 10 through the winding of register 14,to ground.The register 14 charges the call to substation B. Assume next that thecall is originated at the substation A. In this case the closure of thehigh potential test circuit is ineffective to operate either of therelays 22 or 23 since the substation is free fromground connections..When the control switch reaches position 8, however, the circuitpreviously traced from the positive pole of battery 69 extends over thetip conductor of the subscribers line through the switchhook contacts,talking transmitter 72, through the device 1 and returning over the ringside of the line to the opposite pole of battery 69. It is assumed thatdevice 1 is so connected as to permit cur-' 71, through the contact ofrelay 30, contact of relay 26, brush 9, through the winding of theregister 13 to ground.

By employing a directional device at the A substation A which permitscurrents of low potentialto flow through the talking circuit in onedirection and not in the other, a positive test is obtained for thefourth. substation on the party line. Although connected directly to thetalking circuit the directional device 1 offers practically nointerference with the conversational current.

Should a low resistance ground connection be applied to the line, itwill be detected by the operation of one or both of the relays 24 and25. Either one of these relays closes an obvious circuit for relay 29.In this instance the metering circuit leads over conductor 71 throughthe front contact of relay 29 and the winding of relays 32 to ground.closes a circuit to the alarm device 50 to notify the attendantthat-trouble exists on the line.

While the invention has been illustrated as applied to a systememploying a certain type of selective switch it is to be understood thatit is not so limited but may be embodied in various types of systems.Furthermore any discriminating type of directional device may beemployed for the substations B, C and D on the party line.

What is claimed is:

1. The combination in a telephone system of a subscribers line, a testcircuit including the two sides of said line in series, and a device atthe subscribers station allow Relay 32 ing current to flow in onedirection in said circuit and resisting. the flow of current in theother direction. 7

2. The combination in a telephone system of a subscribers line, a testcircuit including the two sides of said line inseries, and a device inthe talking circuit at the subscribers station arranged to permit theflow of cur rent in one direction in said test circuit and to resistflow in the opposite direction.

3. lhe combination in a telephone system of asubscribers line, a testcircuit including. the two sides of said line in series, a device at thesubstation arranged to pass current in one direction in said testcircuit and to oppose the flow of current in the other direction, aregister, and means responsive to current flow in'the test circuit forcontrolling said register.

4. Ina telephone system, a party line,

'means for distinguishing one substation on the line from anothercomprising a test cir cuit including both sides of the line in seriesand a device at the substation arranged to pass current in onedirectionin the test circuit and to oppose current flow in the other direction,means individual to each substation, and means responsive to currentflow in the test circuit lf'or selectively operating said individualmeans.

5. In a telephone system, a line having a plurality of substations,means controlled by the switclihook at any one of said substationsforcloslng a circuit including the two sides of the line in series, anda current con- I trolling device at one of the substations for allowingcurrent to flow in one direction in 6. In a telephone system, a linehaving a plurality of substations" thereon, an asymmetric currentcontrolling, device at each of two substations, one of said devicesincluded in the talking circuit, the other device excluded fromthetalking circuit, and test circuit-s including said devices fordistinguishing; one substation from another.

7. In combination, a party line, an asymmetric current controllingdevice at each of two substations on said. line, a test circuitincluding one of said. devices andthe two sides of the line in series, asecond test circuit including the other device and both sides of theline in parallel, message registers, and means controlled by currentflowing in said test circuits for selectively operating said registers.

8. In combination, a central oflice, a party line, a test circuitincluding both sides of the line in series, a source of potential atsaid otfice,.means for connecting said source in said circuit in onedirection, means for reversing the connection of said source, and adevice included in the test circuit at one ofthe substations forpermittingcurrent to flowin one direction in said circuit and resistingflow in the opposite direction.

In'witness whereof, I hereunto subscribe my name this 17 day of OctoberA. D., 1927.

HERBERT E. BRAGG. I

